Team Fortress 2 is reusing the same contract tracking mechanism from last year's Halloween Event (the Gargoyle) and thus it is showing all the completed Merasmissions from last year as well.
They've also removed the total count from the 'Tome of Merasmissions':
To top it off, new missions keep appearing as I complete them, so I don't even know where I'm up to in general.
How many total Merasmissions are there this year? Is there actually a limit or do they simply continuously spawn?